The invention relates generally to communication systems and, in particular, to a system and method for synchronizing discrete frames of data transmitted as a continuous stream of digital data in a receiver.
The transmission of digital data over a radio frequency communication link is very often implemented by transferring the stream of digital data as discrete packets or frames (as opposed to a continuous homogeneous stream) of information from a transmitter to a receiver. Proper recovery of the digital information depends in part upon the receiver being in sync with the stream of incoming digital data packets. In general, apparatuses for synchronizing frames within a stream of digital data have been known in the art. Most of these prior art apparatuses provide for synchronization occurring at a particular repeating interval during the reception of an incoming digital data stream.
In a digital receiver, frame synchronization refers to determination of the location of a demarcated position within a received bit stream. Demarcation is generally implemented by inserting a fixed pattern of bits, referred to as a “sync word” into the bit stream. Location of the sync word is accomplished by matching a pattern embedded in the bit stream. Pattern matching is commonly performed using two techniques. One technique employs scanning the detected bits and searching for the best match, also referred to as ‘hard match’. Another technique employs a cross-correlation technique on the detected bits, also referred to as ‘soft correlation’.
In many applications, it is known a-priori that the sync word will be transmitted within a certain time period. For such an event, the synchronization decision rule includes an appropriate soft or hard match/correlation metric for all bit positions in the time period and selecting the location with a highest metric. However, in other applications, wherein no a-priori knowledge is available, incoming data stream must be continuously searched, and a “hard” decision must be made at every time position determining whether the sync word is present or not. Such an event results in a complex and time consuming process.
Therefore, an improved frame synchronization technique is desirable to address one or more of the aforementioned issues.